The present invention relates to controlling torque in an internal combustion engine equipped with a hybrid valvetrain in response to a change in operating mode.
There are situations in the operation of an internal combustion engine, which lead to torque disturbances. Examples of situations where a torque disturbance must be managed to provide a smooth torque trajectory are a transition in a variable displacement engine (VDE, an engine in which a portion of the cylinders are deactivated during light load operation to improve fuel economy), a transition in compression ratio in a variable compression ratio (VCR) engine, and a gear shift in a transmission coupled to the engine, termed mode transitions herein. Alternatively, there are situations in which a rapid change in torque is desirable: a traction control event, a driver demand for a rapid change in torque, and other mode transitions.
A method is disclosed for making a mode transition in a multi-cylinder internal combustion engine. The mode transition is one which affects engine torque. Each cylinder is coupled to a fully variable intake valve. The method includes the steps of: determining a desired torque trajectory, determining a next scheduled cylinder due to undergo an intake stroke, computing an intake valve closing time of the fully variable intake valve for he next scheduled cylinder to provide a desired amount of air in the next scheduled cylinder based on the desired torque trajectory, providing an amount of fuel to the next scheduled cylinder in proportion to the desired air, commanding the intake valve closing time to the fully variable intake valve of the scheduled next cylinder; and combusting the fuel and air in the next scheduled cylinder to provide the desired engine torque trajectory.
A valve system in a multi-cylinder internal combustion engine for making a mode transition is disclosed. The mode transition affects engine torque. The system consists of a fully variable intake valve coupled to the cylinder and an engine control unit operably connected to the engine and the fully variable intake valve. The engine control unit determines a desired torque trajectory, determines a next cylinder scheduled to undergo an intake stroke, computes an intake valve closing time of the fully variable intake valve for the next scheduled cylinder to provide a desired amount of air in the next scheduled cylinder based on the desired torque trajectory, computes an amount of fuel to provide to the next scheduled cylinder, and commands the intake valve closing time to the fully variable intake valve of the scheduled next cylinder.
An advantage of the present invention is that torque production can be affected within one engine cycle in an engine with a valvetrain having a fully variable intake valve. The invention may be applied in system where torque changes occur such as VDE, VCR, or by transmission gear shifts.
A further advantage of the present invention is that by providing a variable timing device on the camshaft actuating the intake valve, the engine""s volumetric efficiency is improved which leads to higher peak power.
A further advantage of the present invention is that exhaust pumping work can be minimized and expansion work on the piston can be maximized by optimizing the exhaust valve opening time as a function of engine speed and torque, which is provided by a variable timing device on the exhaust camshaft. Both a reduction in exhaust pumping work and an increase in expansion work improves the overall engine efficiency.
A further advantage of the present invention is that by providing both flexible intake and exhaust timing, the beginning, the end, and the duration of valve overlap are variable, valve overlap being the time over which at least one intake and one exhaust are open simultaneously. The additional flexibility allows more control to simultaneously optimize the amount of exhaust residuals trapped in the cylinder and reduce intake pumping work.
The inventors of the present invention have also recognized that a valve system with a fully variable intake valve and an exhaust cam phaser may be employed to deactivate selected cylinders in an engine to obtain variable displacement engine efficiency improvements.